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    Subject[RFC v3 0/2] Introduce DMA buffer sharing mechanism
    Hello Everyone,

    This is RFC v3 for DMA buffer sharing mechanism - changes from v2 are in the
    changelog below.

    Various subsystems - V4L2, GPU-accessors, DRI to name a few - have felt the
    need to have a common mechanism to share memory buffers across different
    devices - ARM, video hardware, GPU.

    This need comes forth from a variety of use cases including cameras, image
    processing, video recorders, sound processing, DMA engines, GPU and display
    buffers, and others.

    This RFC is an attempt to define such a buffer sharing mechanism- it is the
    result of discussions from a couple of memory-management mini-summits held by
    Linaro to understand and address common needs around memory management. [1]

    A new dma_buf buffer object is added, with operations and API to allow easy
    sharing of this buffer object across devices.

    The framework allows:
    - a new buffer-object to be created with fixed size.
    - different devices to 'attach' themselves to this buffer, to facilitate
    backing storage negotiation, using dma_buf_attach() API.
    - association of a file pointer with each user-buffer and associated
    allocator-defined operations on that buffer. This operation is called the
    'export' operation.
    - this exported buffer-object to be shared with the other entity by asking for
    its 'file-descriptor (fd)', and sharing the fd across.
    - a received fd to get the buffer object back, where it can be accessed using
    the associated exporter-defined operations.
    - the exporter and user to share the scatterlist using map_dma_buf and
    unmap_dma_buf operations.

    Documentation present in the patch-set gives more details.

    This is based on design suggestions from many people at the mini-summits,
    most notably from Arnd Bergmann <>, Rob Clark <> and
    Daniel Vetter <>.

    The implementation is inspired from proof-of-concept patch-set from
    Tomasz Stanislawski <>, who demonstrated buffer sharing
    between two v4l2 devices. [2]

    Some sample implementations and WIP for dma-buf as user and exporter are
    available at [3] and [4]. [These are not being submitted for discussion /
    inclusion right now, but are for reference only]

    [3]: Dave Airlie's:
    [4]: Rob Clark's:

    Patchset based on top of 3.2-rc3, the current version can be found at
    Branch: dma-buf-upstr-v3

    Earlier versions:
    v2 at:
    v1 at:

    Best regards,
    ~Sumit Semwal


    - Review comments incorporated:
    - from Konrad Rzeszutek Wilk []
    - replaced BUG_ON with WARN_ON - various places
    - added some error-checks
    - some cosmetic / documentation comments

    - from Arnd Bergmann, Daniel Vetter, Rob Clark
    - removed mmap() fop and dma_buf_op, also the sg_sync* operations, and
    documented that mmap is not allowed for exported buffer
    - updated documentation to clearly state when migration is allowed
    - changed kconfig
    - some error code checks

    - from Rob Clark []
    - update documentation to allow map_dma_buf to return -EINTR

    - Review comments incorporated:
    - from Tomasz Stanislawski []
    - kzalloc moved out of critical section
    - corrected some in-code comments

    - from Dave Airlie []

    - from Daniel Vetter and Rob Clark []
    - use struct sg_table in place of struct scatterlist
    - rename {get,put}_scatterlist to {map,unmap}_dma_buf
    - add new wrapper APIs dma_buf_{map,unmap}_attachment for ease of users

    - documentation updates as per review comments from Randy Dunlap

    v1: original

    Sumit Semwal (2):
    dma-buf: Introduce dma buffer sharing mechanism
    dma-buf: Documentation for buffer sharing framework

    Documentation/dma-buf-sharing.txt | 222 ++++++++++++++++++++++++++++
    drivers/base/Kconfig | 10 ++
    drivers/base/Makefile | 1 +
    drivers/base/dma-buf.c | 289 +++++++++++++++++++++++++++++++++++++
    include/linux/dma-buf.h | 172 ++++++++++++++++++++++
    5 files changed, 694 insertions(+), 0 deletions(-)
    create mode 100644 Documentation/dma-buf-sharing.txt
    create mode 100644 drivers/base/dma-buf.c
    create mode 100644 include/linux/dma-buf.h


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